a. Field of the Invention
The present invention relates generally to cargo systems for aircraft, and, more particularly, to a system that enables containerized cargo to be stowed in an upper, generally overhead area of an upper lobe of a fuselage of an aircraft.
b. Related Art
For reasons of economy or flexibility, it is often desirable to convert a passenger aircraft to transport cargo. Conversions may be permanent or temporary/reversible, and moreover may involve the entire aircraft or only a part of it. As a general rule, however, it is desirable that such conversions be economical in nature, and in particular that modifications to the existing air frame and systems be kept to a minimum. Low weight is also a desirable characteristic.
Another important factor is maximum utilization of available space. In this regard, it will be understood that in the case of cargo aircraft, volume rather than weight is often the limiting factor, and so for efficient operation it is therefore generally important to be able to fill as much as possible of the interior volume of the fuselage with cargo.
Achieving the above goals is complicated by certain realities of the aviation industry. First, it will be understood that in modern operations most of the cargo is not packed “bulk” into the fuselage, but instead is first placed into containers that are loaded into the aircraft in a modular fashion. The containers typically have configurations that are standardized (e.g., “LD6”), at least by aircraft type, and generally have a somewhat rectangular geometry, sometimes being angled or “beveled” at one or both lower/outboard edges to better fit within the confines of the cargo holds in the lower lobe.
As another factor, it will be understood that aircraft initially configured for passenger use typically only have hatches capable of receiving such containerized cargo in the lower lobe of the fuselage, with access to the upper lobe/main deck of the aircraft being limited to smaller doors designed primarily for passenger ingress/egress and/or loading of in-flight service items. Adding cargo-loading hatches to the upper lobe of an existing aircraft generally requires modifications that would render such a conversion unattractive from a cost standpoint, and furthermore the ability to return the aircraft to a satisfactory passenger-carrying configuration would be significantly compromised. Moreover, the existing equipment of many airport facilities are designed primary to load cargo through lower lobe hatches, rendering the advantages of upper lobe cargo hatches moot.
One approach towards loading cargo into the upper lobe of an aircraft while meeting the above constraints has been to employ a lift mechanism that moves the containers from the lower lobe to the upper lobe after they have been loaded into the latter, and vice-versa during unloading. A non-limiting example is the lift system that is shown in U.S. Pat. No. 8,011,617, which is incorporated herein by reference. The structural modifications involved in such an approach are mostly limited to the main deck of the aircraft, to provide an opening for the cargo lift, and major changes to the skin and frames of the fuselage are generally avoided.
A remaining problem, however, has been that even after the cargo containers have been loaded onto the upper, main deck of the aircraft, much of the available space remains unfilled. It will be appreciated that in passenger aircraft the main deck, which forms the floor of the passenger compartment, is generally positioned well below the mid-level of the fuselage, to provide adequate space of the passengers and their luggage, as well as for various overhead systems; consequently the height of the underlying cargo compartments is typically much less than that of the passenger compartment. As a result, since the height of the cargo containers is necessarily constrained by the height of the cargo compartments, the containers are insufficiently tall to fill the full height of the passenger compartment when they are moved to the main deck, so that an upper, overhead area of the fuselage remains unfilled. This problem is particularly acute in the case of wide body aircraft such as the Boeing B-777, with the result that a single height row or rows of conventional containers will leave a great portion of the upper lobe unfilled.
Accordingly, there exists a need for a system for carrying cargo in an upper, overhead area of the upper lobe of the fuselage of an aircraft, so as to make efficient use of available volume within the fuselage. Furthermore, there exists a need for such a system that allows the space in the upper portion of the upper lobe to be filled with cargo in modular containers. Still further, there exists a need for such a system in which such containers are loaded into the aircraft through cargo doors providing access to one or more cargo compartments in the lower lobe of the fuselage. Still further, there exists a need for such a system that does not require major modification of existing structures and systems of the aircraft, particularly an aircraft previously configured for passenger-carrying operation. Still further, there exists a need for such a system that facilitates efficient performance of functions by both flight crew and ground service personnel. Still further, there exists a need for such a system that is light in weight, and economical to construct and install.